The research being proposed is to carry out an analysis of the method being used for data reduction in a longitudinal, ethological study of language development in four middle class and four lower class infants from 10 weeks of age until they meet certain competence criteria for verbal participation in interactive episodes with their mothers. The criteria are phonological, syntactic, pragmatic (functional) and discourse related. Data are video and audio tapes made biweekly in the infant's home as the mother goes about the daily routine of undressing, bathing, dressing and feeding the infant. Mother and infant contributions to the interaction are categorized according to a four dimensional analytic system which includes the categorical behaviors in each dimension along with all the other behaviors deemed relevant to the analysis. Ultimatyely a time series analysis model will be used to test the generality of orders of emergence of criterial behaviors over infants and the independence of infant development of criterial behaviors from mother behaviors. The purpose of the analysis of data reduction methodology being proposed is to investigate whether use of the methodology picks out systematic changes and/or consistencies in the language and related behavior of infants and relationship to mother behaviors. The data from the videotapes at 3, 6, 9, 12, 15, 18, and 24 months for each infant will be analyzed in this study.